BackgroundWorker 更改标签多线程VB.NET

Question

我是多线程和后台工作者的新手。我试图根据教程和论坛主题编写一个简单的测试，但它没有按我预期的那样工作。

我有一个带有 Button1、Label1、BackgroundWorker1 控件的 windows 表单应用程序。

我想在单击按钮时执行此操作：

后台工作人员不断检查变量state True 或 False
首先将标签文本更改为 False（第一次状态 = false）
如果state在主线程中设置为True，将标签文本更改为True（state在"Sample process"（For Next）结束时设置为True）

我的代码是：

Public state As Boolean
Public Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Debug.Print("Button1_Click ThreadID - " & Thread.CurrentThread.ManagedThreadId)
    state = False

    BackgroundWorker1.RunWorkerAsync()

    '--Sample process in the main thread
    For c = 0 To 10000
        Debug.Print(c)
    Next

    state = True

End Sub


Dim c As Integer
Public Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork


    setlabel(state.ToString)

    Do While state = False
        Debug.Print("BackgroundWorker1_DoWork ThreadID - " & Thread.CurrentThread.ManagedThreadId & " - state: " & state)
        Thread.Sleep(100)
    Loop

    setlabel(state.ToString)
End Sub

Public Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    Debug.Print("BackgroundWorker1_RunWorkerCompleted - State: " & state)

End Sub

Sub setlabel(text As String)
    Label1.Invoke(Sub()
                      Label1.Text = text
                  End Sub)
End Sub

我的问题是：

标签的文本在开始时没有更改为 False BackgroundWorker1_DoWork
在Do While中没有Debug.Print

输出为：

Button1_Click ThreadID - 9
0
1
2
...
9998
9999
10000
BackgroundWorker1_RunWorkerCompleted - State: True

我做错了什么？

Answer 1

您正在使用 For 循环占用 UI 线程：

For c = 0 To 10000
    Debug.Print(c)
Next

您需要让 UI 线程空闲以便调用 setlabel(state.ToString) 以实际更新 UI。

所以你需要有一个类似计时器的东西（或者甚至是第二个后台工作者）在设置之前等待一段时间 state = True。

BackgroundWorker 更改标签多线程VB.NET

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